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Tractor Talk Discussion Forum

Snowplow truck hydr. problem

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Roy Suomi

12-06-2006 16:46:41




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O.K. hydraulic guru's....I've been dealing with a hydraulic problem on a Ford F-550 dump truck..The engine mounted Deweze hydraulic system uses a Parker-Commercial gear pump..I've been having a reoccuring problem with the pump shaft seal..It actually pushes the lips of the seal outward , causing a leak. In order to operate the dump bed [with a direct push cylinder , not scissor hoist ]The pressure must be set at 2250 minimum..I've been through everything I can think of..I took the main valve out and disassembled it , found nothing..Took the spreader valve out and found nothing...Took hoses off and blew through them..Changed return filter , no difference..Now the P.O.S. did it again.. It appears that the pump is designed to bypass oil through the idler gear shaft and return the oil to the suction side of the pump so it doesn't overpressure the shaft seal..For some reason this seal is getting too much oil pressure or flow volume that the drilled gear shaft can't handle..I've been told that Parker-Commercial has an improved inner seal [ bronze plates] that's supposed to take care of this..Anyone heard of this?? How about other ideas??

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George G

12-07-2006 11:40:50




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 Re: Snowplow truck hydr. problem in reply to Roy Suomi, 12-06-2006 16:46:41  
Sounds to me like you might be running a clockwise rotation pump counterclockwise. the only way we are going to know that is if you post the numbers off the pump.(example Parker P/N D22AA1D) The 1 in the example indicate's this pump is CCW rotation. A 2 in that spot would indicate CW rotation.



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jdemaris

12-07-2006 06:08:00




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 Re: Snowplow truck hydr. problem in reply to Roy Suomi, 12-06-2006 16:46:41  
What Mr.Schwiebert stated is correct. Regardless if the gear pump is a Webster Electric, Cessna, Parker, etc. - the external shaft seal is not intended to seal against pressure oil - only residual. And - with all the Parker gear pumps, I don't believe they ever made one rated at lower than 2500 PSI contant duty - and most commercial rated pumps are rated at 4000 PSI or more - constant duty. Anytime a gear pump starts pushing out the seal - it is an indicator of #1 a worn out pump, or #2 the working pressure exceeds the rated PSI limit. Both situations are, more-or-less, the same - since a when a pump wears, it's working PSI limit decreases. The high pressure sealing is supposed to be done by the smooth face of the gear against the pump housing or thrust plate. On some model pumps, there is a replaceable thrust plate sealed by o-rings or a spider gasket - and on other pumps - nothing is replaceable. So, it possible to exceed the rated pressure and blow a gasket - which can be fixed. It's also common for the pump to get scored, bushings wear, etc. - and the pump is unrepairable junk. Some Parker gear pumps have internal pressure relief valves.

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J Schwiebert

12-06-2006 17:32:55




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 Re: Snowplow truck hydr. problem in reply to Roy Suomi, 12-06-2006 16:46:41  
Oh the problems of a former life time! Have you had the pump off and inspected the inside of the pump? Is this a P20 pump and then what width gears or what is the width of the center section? Are you putting stress on one side of the pump shaft because of belt tension? Two other comments. A common cause of front seal failure on a gear pump is too much internal pump leakage. Can you load test the pump? Next thing , this was true with Gresen and I am sure it was with Commerical since that was their major competitor (now also part of Parker) can you get a front seal for a M-20 motor if that is what you have? Motor seals for the output shaft are designed for higher flows and pressures. How much pressure do you run when the control valve is in neutral? Do you need a comerical shop manual for that pump? I should have some left. More questions? J.

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KBS

12-06-2006 17:31:54




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 Re: Snowplow truck hydr. problem in reply to Roy Suomi, 12-06-2006 16:46:41  
I do not think there is a relief valve in this pump, It should be in the valve and 2250 PSI is an awful lot of pressure for this system



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IaGary

12-06-2006 17:19:58




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 Re: Snowplow truck hydr. problem in reply to Roy Suomi, 12-06-2006 16:46:41  
2250# seems like a lot of pressure.

What diameter is the cylinder?

With a 4" cylinder and 2250# pressure you can lift 28,000 pds.

Can't think you are hauling 14 ton in the box on a 550.

Is that the factory pressure setting on the pump?

Gary



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